The present invention relates generally to controlling an economizer circuit in a chiller system. More specifically, the present invention relates to controlling the economizer circuit of a chiller system by controlling a valve for the economizer port of a compressor.
In refrigeration and chiller systems, a refrigerant gas is compressed by a compressor and then delivered to the condenser. The refrigerant vapor delivered to the condenser enters into a heat exchange relationship with a fluid, e.g., air or water, and undergoes a phase change to a refrigerant liquid. The liquid refrigerant from the condenser flows through a corresponding expansion device(s) to an evaporator. The liquid refrigerant in the evaporator enters into a heat exchange relationship with another fluid, e.g. air, water or other secondary liquid, and undergoes a phase change to a refrigerant vapor. The other fluid flowing through the evaporator is chilled or cooled as a result of the heat-exchange relationship with the liquid refrigerant and is then typically provided to an enclosed space to cool the enclosed space. Finally, the vapor refrigerant in the evaporator returns to the compressor to complete the cycle.
To provide increased capacity, efficiency and performance of the refrigeration or chiller system, an economizer circuit can be incorporated into the system. An economizer circuit can typically include an economizer heat exchanger or flash tank, an inlet line to the flash tank that is connected to the condenser or to the main refrigerant line downstream of the condenser, an economizer expansion device, which is incorporated in the inlet line, a first outlet line from the flash tank that is connected to the main refrigerant line upstream of the expansion device, and a second outlet line from the flash tank that is connected to a port within the compression chamber of the compressor or to the suction inlet of the compressor.
In flash tank economizer circuits, liquid refrigerant from the condenser flows through the inlet line and expansion device into the flash tank. Upon passing through the expansion device, the liquid refrigerant experiences a pressure drop, whereupon, at least a portion of the refrigerant rapidly expands or “flashes” and is converted from a liquid to a gas. The liquid refrigerant in the flash tank collects at the bottom of the flash tank and returns to the main refrigerant circuit through the first outlet line. The first outlet line may incorporate one or more valves to control the amount of liquid refrigerant returned to the main refrigerant circuit. The gaseous refrigerant in the flash tank collects at the top of the flash tank and returns to the compressor through the second outlet line to either the suction inlet or the compression chamber, usually to a point in the compression chamber at an intermediate pressure. The second outlet line may also incorporate one or more valves to control the amount of gaseous refrigerant provided to the compressor.
As discussed above, an economizer circuit can be used to provide increased capacity, efficiency and performance of the refrigeration or chiller system. For example, the economizer circuit can improve system efficiency by providing refrigerant gas at an intermediate pressure to the compressor, thereby reducing the amount of work required by the compressor and increasing compressor efficiency. A variety of parameters in the economizer circuit can be controlled to provide the increased capacity, efficiency and performance of the refrigeration or chiller system. In particular, the amounts of refrigerant entering and leaving the flash tank can be controlled, as well as the amount of liquid refrigerant in the tank, to obtain the desired capacity, efficiency and performance of the refrigeration or chiller system.
Therefore, what is needed is a system and method for simply and easily controlling an economizer circuit to provide improved performance to a refrigeration or chiller system.